The invention relates to a method for determining a personalized cardiac model using a magnetic resonance imaging sequence.
The field of the invention is, but not limited to, the imaging of the heart with Magnetic Resonance Imaging (MRI) techniques.
The movement of the heart is relatively periodic and can be understood as the repetition of cardiac cycles. However, within a cardiac cycle, this movement is quite complex and physiologists have defined several cardiac phases. Depending on the level of precision wanted, the cardiac cycle may be divided into different numbers of phases.
The simplest division is systole for contraction vs. diastole for relaxation. However, systole may also be divided into isovolumic contraction (before opening of the output valve) and ejection (after opening of the output valve). In a similar way, diastole may be divided in at least five phases: isovolumic relaxation, early ventricular filling, diastasis, auricular ejection, auriculoventricular delay.
The division of cardiac cycles into a given number of phases and the prediction of the duration of these phases when heart rate changes from beat to beat is called “cardiac model”.
Magnetic Resonance Imaging (MRI) techniques are very efficient techniques for the functional exploration of the heart. But they are facing the problem that the acquisition of the data is made slice by slice in a time-consuming process. Without specific precautions, the images of a moving organ such as the heart may be blurred. So imaging methods have been developed, which use the periodical nature of the heart beat to synchronize the acquisitions.
Cardiac Magnetic Resonance (CMR) imaging is based either on cine acquisition (producing a video with several frames of a mean cardiac cycle) which is considered the gold-standard to quantify left ventricle volume, ventricle mass and stroke volume, or on acquisition of static images which are very useful to characterize myocardial tissue and to detect for example oedema or fibrosis.
In both cases, CMR requires a cardiac model (the knowledge of the durations of each cardiac phases), either to determine a cardiac “rest” period in which data can be acquired with minimal motion (for cardiac triggered types of acquisition like black blood, T1 and T2 maps, Late Gadolinium Enhancement, coronaries, etc.) or to attribute acquired k-space lines to cardiac phases in retrospective reconstruction of cine acquisitions. This is especially important for high temporal resolution cine acquisitions.
However, the known cardiac models are not patient-adaptive.
The currently published cardiac model used in the context of cine MRI is a linear stretching of the systole and diastole periods separately. Although this model seems to be the most recent one and is used routinely and worldwide for cine reconstructions, it is based on data acquired 45 years ago with a technology now considered obsolete. In this study, a linear fit on inter-individual values was performed within a cohort of subjects. This model predicts the mean duration of systole and diastole within a general population. However, this model was not designed to predict variations within different cardiac cycles of a single subject. It cannot cope with physiological differences among subjects due for example to pathological conditions, diurnal variation in the systolic intervals, pressure changes or medication that alter systolic or diastolic times.
It is for instance known that equations from males and females differ slightly, and that the left ventricular ejection duration increases independently from heart rate from infancy to puberty and is prolonged in the elderly.
It is an object of the invention to provide a method for the construction of a personalized cardiac model adapted to each subject.
It is also an object of the invention to provide a method for the construction of a personalized cardiac model whose parameters are adjusted to meet the particular patient's cardiac cycles instead of using generic and fixed parameters extracted from a whole cohort.
It is also an object of the invention to provide a method for the construction of a personalized cardiac model which allows improving the prediction of the rest time period where imaging should be done for triggered MRI sequences.
It is also an object of the invention to provide a method for the construction of a personalized cardiac model which allows improving the time resolution precision in MRI cine retrospective reconstructions.